(a) Technical Field
The present invention relates to a battery charging system using a charger and a driving control method of the charger thereof, which increases the driving time of the charger during a power failure of the charger mounted within a vehicle.
(b) Background Art
As air pollution caused by exhaust gas of vehicles increases due to the development of automobile industries, interest in reduction of the exhaust gas has increased. Thus, studies on environmentally-friendly vehicles capable of reducing exhaust gas have been actively conducted. The environmentally-friendly vehicles include a hybrid vehicle, a plug-in hybrid vehicle, an electric vehicle, a fuel cell vehicle, and the like. Among these vehicles, the plug-in hybrid vehicle and the electric vehicle perform battery charging using a power source. Accordingly, an on board charger (OBC) is mounted within the vehicle.
FIG. 1 is an exemplary configuration diagram illustrating a battery charging system using an OBC according to a related art. FIG. 2 is an exemplary graph illustrating states of factors (e.g., output voltage, output current, output power, and the like) related to driving of the charger when an instantaneous power failure of charger input power occurs in the battery charging system. In particular, the graph (a) in FIG. 2 illustrates a state of alternating current (AC) input voltage VIN input to the OBC and graph (b) illustrates a state of output voltage Vo of the OBC. In addition, graph (c) illustrates a state of output voltage VDC of a power factor corrector (PFC) of the OBC, graph (d) illustrates a state of output current Io of the OBC, graph (e) illustrates a state of output power Po of the OBC, and graph (f) illustrates a state of effective duty Deff for controlling the output voltage of a DC-DC converter.
The related art battery charging system using the OBC is used to charge a high voltage battery used as a main battery of an environmentally-friendly vehicle. As shown in FIG. 1, the battery charging system includes a PFC converter 1, a direct current-direct current (DC-DC) converter 2, a controller 3, a first capacitor 4, and a second capacitor 5.
The PFC converter 1 is connected to an output terminal of an AC power unit 6 to convert AC input voltage VIN input from the AC power unit 6 into DC voltage VDC and compensate for the power factor of power. The DC-DC converter 2 is connected between an output terminal of the PFC converter 1 and an input terminal of a high voltage battery 7 to receive DC voltage VDC output from the PFC converter 1 to convert the DC voltage VDC into voltage for charging of the high voltage battery 7. In particular, an insulated DC-DC converter using a full-bridge or half-bridge type switching circuit may be applied to the DC-DC converter 2.
The first and second capacitors 4 and 5 smooth outputs of the PFC converter 1 and the DC-DC converter, respectively. The graphs of the output voltage VDC of the PFC converter 1 and the output voltage Vo of the DC-DC converter 2 (or the OBC), shown in FIG. 2, illustrate voltages smoothed through the use of the first and second capacitors 4 and 5. The controller 3 is configured to receive the AC voltage VIN output from the AC power unit 6 and the output voltage VDC of the PFC converter 1 to operate the PFC converter 1, and receive the output voltage Vo of the DC-DC converter 2 to operate the DC-DC converter 2. In particular, the PFC converter 1 is configured to receive input current input from the controller 3, and the DC-DC converter 2 is configured to receive output current input from the controller 3.
The related art battery charging system configured as described above uses a control technique of maintaining the existing state when the supply of the AC input voltage to the OBC is stopped due to an instantaneous power interruption or power failure, (i.e., a control technique of maintaining a driving state of the OBC to be identical to that before the supply of the AC input voltage VIN of the OBC is stopped). Specifically, in the OBC shown in FIG. 1, the output voltage VDC of the PFC converter 1 is used as an input voltage of the DC-DC converter 2. Thus, the output voltage VDC becomes an important factor for determining a driving time of the charger.
In the battery charging system, the minimum voltage VDC_min capable of continuously driving the OBC should be maintained to a few microseconds (μs) or greater to prevent malfunction and damage of the OBC by detecting and storing the driving state of the OBC when the input of the charger is stopped. When the power supply is stopped due to the AC input voltage VIN of the OBC being turned off, this is the same as no input voltage VIN of the PFC converter 1. Hence, the PFC converter 1 is in an uncontrollable state due to loss of input, and the controller 3 may not be able to adjust the output voltage VDC of the PFC converter 1.
In other words, in the related art battery charging system, the charging operation of the OBC is controlled identically to the existing state (state in which the AC input voltage is on) even though the AC input voltage VIN is off, and therefore, the voltage of the first capacitor 4 is suddenly decreased. As a result, the output voltage VDC of the PFC converter 1 decreases to less than the minimum voltage VDC_min. Therefore, a minimum driving time for detecting and dealing with the driving state of the charger may not be possible. When the OBC mounted in the vehicle does not receive the input voltage VIN due to an instantaneous power failure or the like, the driving state of the OBC is not precisely detected. As a result, a malfunction of the OBC may be caused, and therefore, the vehicle may be in a dangerous situation.
Accordingly, in the related art battery charging system, a method of increasing energy stored in the first capacitor 4 by increasing the capacity of the first capacitor 4 is used to delay the time at which the output voltage VDC of the PFC converter 1 reaches the minimum voltage VDC_min and to secure the minimum driving time of the OBC when the supply of the AC input voltage VIN is stopped. However, this causes an increase in cost.